Description of the Prior Art
This invention relates to a yarn draw off tube for an open-end spinning unit.
It is desirable to produce a soft twist yarn having less fluffs by means of a rotor-type open-end spinning unit. However, it is very difficult to produce such a yarn of an evenly distributed less twist as mentioned above by means of an open-end spinning unit for various reasons. First, in an open-end spinning unit, a fiber ribbon deposited on a fiber-collecting surface of a spinning rotor is twisted to form a yarn due to rotation of the spinning rotor while the fiber ribbon is being drawn off from the rotor. The root portion of the yarn which merges into the fiber ribbon on the fiber-collecting surface has less of a twist density than does the other portion of the yarn, and, therefore, yarn breakage often occurs in this portion. This tendency is naturally remarkable in the case of soft twist yarn. To improve the twist density of the yarn root portion, various proposals have been made. For example, in Japanese Unexamined Patent Publication (Kokai) No. 49-132329, a yarn draw off tube provided with a high frictional surface is disposed so as to confront the spinning rotor, thereby imparting a false twist to the yarn. Further, in Japanese Examined Patent Publication (Kokoku) No. 43-24978, an eccentric yarn draw off tube is proposed for improving the twist transmission to the root portion of the yarn. In the case of the former yarn draw off tube, however, the produced yarn becomes fluffy or has snarled fibers in its structure due to excessive rubbing of the frictional surface. In the case of the latter tube, the twist is not satisfactorily transmitted. On the contrary, the yarn tension fluctuates sharply, thereby causing yarn breakage or an uneven thickness.